On applications for organic secondary batteries, in 1967 M. Jozefowicz et al. (French Pat. N.P. 95630) innovated in using polyaniline (PAn) as the battery electrode and expanded the development of the organic battery. In 1981, A. G. MacDiarmid et al. (J. Chem. Soc. Chem. Commun., (1981) 317) successfully used electrochemically doped polyacetylene (PA) as the electrode of an organic secondary battery. And E. M. Genies et al. (Mol. Cryst. Liq. Cryst., 121 (1985) 181; Mol. Cryst. Liq. Cryst., 121 (1985) 195) used p-type doped polyaniline as the positive electrode and lithium as the negative electrode to form an organic secondary battery with high energy density and cycle life. Goto et al. (J. Power Sources, 20 (1987) 243) found that among the secondary batteries with PAn, PA, polypyrroles (PPy), polythiophene (PT), etc. as electrodes, the one with PAn has the best performance. It has the advantages of high energy density, power density, capacity efficiency, long cycle life and low self-discharge.
So far, organic secondary batteries, which use polyaniline as the battery plate, can be classified into three major categories. The first group are secondary batteries containing aqueous electrolyte [A. G. MacDiarmid et al., Mol. Cryst. Liq. Cryst., 121 (1985) 187; A. Kitani, M. Kaya, and S. Sasaki, J. Electrochem. Soc., 133 (1986) 1069; N. L. D. Somasiri et al., J. Applied Electrochemistry, 18 (1988) 92; A. G. MacDiarmid et al., U.S. Pat. No. 5,023,149 (1991); F. Trinidad et al., J. Electrochem. Soc., 138 (1991) 3186]. The second group are organic secondary batteries containing non-aqueous electrolyte [A. Kitani et al., Bull. Chem. Soc. Japan, 57 (1984) 2254; E. M. Genies et al., Synthetic Metals, 18 (1987) 631; F. Goto et al., Synthetic Metals, 18 (1987) 365; Ricoh Co. U.S. Pat. No. 5,037,713 (1991)]. The third group are organic secondary batteries containing solid polymeric electrolyte [Hydro-Quebec, U.S. Pat. No. 4,758,483; C. Arrbizzani et al., Synth. Met., 28 (1989) C663; Li Changzhi et al., J. Power Sources, 39 (1992) 255; T. Ohsawa et al. (Ricoh Corp.) Synthetic Metals, 41 (1991) 3021]. In non-aqueous media, usually lithium was used as the negative electrode because of its highest oxidation potential, and light weight and easy for extension. It not only provides an increased open circuit voltage (Voc), but also an elevated unit mass charge capacity. When aqueous solution is used as the electrolyte, the negative electrode material should be metal with a lower oxidation potential (such as Zn, Al). This makes the open circuit voltage (1.0 V) and the energy density (100 Whr/kg) lower than those of the non-aqueous battery. Therefore, the organic secondary batteries with non-aqueous electrolyte are of more practical value. The electrolyte can also be a solid. it is composed of polyethylene oxide (PEO) or its copolymer with salt. It provides the advantages of higher stability at high voltage and reduced demand in electrolyte quantity. However, it is of practical use only at temperatures above 60.degree. C. (M. Duval et al. (Hydro-Quebec), Makromol. Chem., Makromol. Symp., 24 (1989) 151).
The synthesis methods of polyaniline include the chemical method [J. Langer, Solid State Commun., 26 (1978) 839; M. Jozfowicz, J. Polymer Sci., C22 (1969) 1187; J. P. Travers et al. Mol. Cryst. Liq. Cryst., 121 (1985) 195) and the electrochemical method (D. M. Mohilner et al., J. Am. Chem. Soc., 84 (1962) 3618; E. M. Genies et al., Mol. Cryst. Liq. Cryst., 121 (1985) 181]. The doped polyaniline powder made by the chemical method can not be dissolved in common organic solvents, which limits its practical applications. In 1987, A. G. MacDiarmid et al [Synth. Met., 21 (1987) 181] first found that de-doped polyaniline powder can be dissolved in NMP (1-methyl-2-pyrrolidinone) and then can be cast into film. NMP is the only known organic solvent that can completely dissolve polyaniline. In 1991 R. L. Elsenbaumer (U.S. Pat. No. 5,006,278) proposed that the polyaniline powder can be dispersed in nitromethane in the presence of ferric chloride, in which the polyaniline is simultaneously doped and dissolved. In 1990, Bridgestone Co. (U.S. Pat. No. 5,066,556 (1991); U.S. Pat. No. 4,957,833 (1990)) used the polyaniline deposited on a current collector, which was synthesized electrochemically, together with lithium (or lithium alloy) as counter electrode to compose of a button battery having a discharge capacity of 80 Ahr/kg. The drawback of this method is that to produce an organic secondary battery with a large electrode area is difficult. Recently Ricoh Co. [U.S. Pat. No. 4,999,263 (1991); U.S. Pat. No. 4,948,685 (1990)] has used the electrochemical method to synthesize a polyaniline film of 0.05 mm thick on a porous metallic film as working electrode and to produce a film battery with outside dimensions of 50 mm long, 50 mm wide and 0.9 mm thick. The battery has an energy density of 326 Whr/kg. However, the polyaniline film is brittle and can not be wound. So far, the known methods to produce a polyaniline electrode in a polyaniline secondary electrode include the following:
(1) Using the chemical method to synthesize polyaniline, mixing the doped polyaniline powder with carbon black and binder and casting the resulting mixture into a film, and pressing the film to adhere on a metallic grid. The metallic grid here is used as a current collector (A. G. MacDiarmid et al., Synthetic Metals, 18 (1987) 393; E. M. Genies et al., J. Applied Electrochemistry, 18 (1988) 751; M. Mizumoto et al., Synthetic Metals, 28 (1989) C639) PA1 (2) Using the electrochemical method to synthesize polyaniline film on a metal substrate. The metal substrate here also serves as a current collector. The polyaniline film synthesized by the electrochemical method has a porous fibrilar structure similar to polyacetylene, and has a large specific area. The film has a large contact area with the electrolyte solution, allowing a high diffusion rate of the charge carriers into the film so as to increase the mass charge capacity of the produced battery (F. Goto et al., J. Power Sources, 20 (1987) 243; S. Tangnshi et al., J. Power Sources, 20 (1987) 249; E. M. Genies et al., Synthetic metals, 29 (1989) C647; Susumu Yonezawa et al., J. Electrochem. Soc., 140 (1993) 629; Bridgestone Corp. U.S. Pat. No. 5,066,556 (1991); U.S. Pat. No. 4,906,538 (1990); U.S. Pat. No. 4,939,050 (1990); Ricoh Corp. U.S. Pat. No. 4,999,263 (1991); U.S. Pat. No. 4,948,685 (1990)). PA1 (1) Using polyaniline synthesized by the chemical method to produce the electrode. PA1 (2) Using polyaniline synthesized by the electrochemical method to produce the electrode plate.
There are many drawbacks in the two methods for producing polyaniline electrodes as described below:
1. The polyaniline synthesized by the chemical method is in powder form and requires pressing to form a film. The polyaniline electrode so produced has a weak mechanical strength and is easy to crack under stress. PA2 2. Since the polyaniline powders are adhered together through the use of polymeric binder and then pressed with the current collector to give a working electrode, the contacts among the polyaniline powders and between the polyaniline and current collector are poor. Thus, the internal resistance of the electrode is increased and the battery performance is decreased. PA2 3. The polyaniline synthesized by the chemical method has a surface morphology more compact than that synthesized by the electrochemical method. The contact area of the electrode with the electrolyte solution is therefore smaller. During the process of charging and discharging, the ion diffusion resistance is greater; therefore, the battery performance is lower. PA2 4. The method can not produce an electrode of large area; therefore, its practical value is limited. PA2 1. The polyaniline synthesized by the electrochemical method is difficult to be used for preparing a battery electrode with large area. Therefore currently there is only button type battery available in the market [Bridgestone Corp. U.S. Pat. No. 4,957,833 (1990)]. PA2 2. The process for producing polyaniline by the electrochemical method is more complicated than that of the chemical method. PA2 3. The polyaniline film produced by the electrochemical method is brittle and is easy to be broken by external force. Therefore, to prepare a wound-type battery is impossible.
The main objective of this invention is to provide electroconductive polymer composites for use in secondary batteries as positive electrode active materials. The composites have characteristics including excellent mechanical properties, conductivity, and large specific contact area between the electroconductive polymer and the electrolyte.
Another objective of this invention is to provide a positive electrode for a secondary battery without the drawbacks specified above.
Still another objective of this invention is to provide a non-aqueous secondary battery which has high open-circuit-voltage (Voc), high energy density, high charge capacity, and good stability of charge capacity.